In vitro susceptibility of Capnocytophaga species to 29 antimicrobial agents

Antibiotic Resistance among Fusobacterium, Capnocytophaga, and Leptotrichia Species of the Oral Cavity

PURPOSE

Antibiotics play an important role in treating periodontal diseases. Due to the effectiveness of antibiotic therapies, their usage in dentistry has significantly increased. The aim of this study focused on the in-vitro susceptibility of different gram-negative oral bacteria species - which are associated with periodontal diseases (Fusobacterium spp., Capnocytophaga spp. and Leptotrichia buccalis) and have different geographical origins (Asia and Europe) - against antimicrobials that are clinically relevant in dental therapy.

MATERIALS AND METHODS

A total of 45 strains were tested (29 Fusobacterium spp., 13 Capnocytophaga spp. and 3 L. buccalis) that were either isolated from Chinese patients or were obtained from different strain collections. Their antimicrobial susceptibility to the antimicrobial agents benzylpenicillin, amoxicillin, amoxicillin-clavulanic acid, ciprofloxacin, moxifloxacin, clindamycin, doxycycline, tetracycline and metronidazole was tested using the E-Test. Strains with particular resistance to penicillin, clindamycin and metronidazole were further analysed for resistance genes.

RESULTS

All tested bacterial isolates were sensitive to amoxicillin, amoxicillin-clavulanic acid, doxycycline and tetracycline, but showed variable sensitivity towards other antibiotics such as benzylpenicillin, ciprofloxacin, moxifloxacin, clindamycin and metronidazole.

CONCLUSION

The results of the present study suggest that certain periodontal disease-related bacterial strains can be resistant towards antimicrobial agents commonly used in adjuvant periodontal therapy.

A case of septic arthritis caused by Capnocytophaga canimorsus in an HIV patient

Invasive infections caused by Capnocytophaga canimorsus, a Gram-negative rod found in the oral cavity of healthy dogs and cats, are rare but they are increasing worldwide. We report a case of septic arthritis in a native knee joint due to this micro-organism. A 57-year-old man, with a well-controlled chronic HIV infection, attended the Emergency Department because of left knee pain and shivering without measured fever. A knee arthrocentesis and a computed tomography scan were performed, revealing septic arthritis with collections in the left leg posterior musculature. He was admitted to the Infectious Diseases Department for antibiotic treatment. Initial synovial fluid was inoculated in blood culture bottles, and the anaerobic one was positive after 63 h. Gram stain revealed fusiform Gram-negative rods, identified as C. canimorsus by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) directly from the bottle. Identification was confirmed by 16S rRNA sequencing and serotyping was performed by PCR, with serovar A as the outcome. Due to an unfavourable clinical course, the patient required two surgical cleanings and after appropriate antibiotic treatment he was discharged 2 months later.

Keratocyst Capnocytophaga superinfection

INTRODUCTION

Capnocytophaga spp are Gram-negative bacteria that cause severe infections in immunosuppressed patients. This situation is extremely rare in immunocompetent patients.

CASE REPORT

This clinical report describes the unusual infection of an immunocompetent patient with Capnocytophaga spp. The imaging studies showed the existence of a cyst in the left jawbone. After treatment and a microbiological study of the content, it was found to be an outbreak of septicaemia.

DISCUSSION

Capnocytophaga spp, commensal bacteria of the oral cavity, can lead to serious illness and that is why an empirical treatment is needed until a diagnostic confirmation can be obtained.

Capnocytophaga keratitis in dogs: clinical, histopathologic, and microbiologic features of seven cases

OBJECTIVE

To describe the clinical, microbiologic, and histopathologic features of Capnocytophaga keratitis in dogs.

ANIMALS STUDIED

Seven dogs with naturally acquired Capnocytophaga keratitis.

PROCEDURES

Medical records of dogs with a clinical diagnosis of keratitis and corneal cultures positive for Capnocytophaga spp. were reviewed. Dog signalment, medical history, clinical findings, and diagnostic assay results were recorded.

RESULTS

Breeds included Boston terrier (n = 3 dogs), Rat terrier (n = 2), and single cases of mixed breed and Pug. All dogs examined had expansive corneal ulceration involving the majority of the corneal surface. Marked corneal infiltrates, keratomalacia, and hypopyon were present. Progression of corneal disease was rapid with extensive dissolution of the corneal stroma. Corneal lesions progressed to catastrophic perforations within 24 h of the initial examination in three dogs, requiring enucleation. One globe was enucleated after failure to resolve with long-term medical therapy. Globes and vision were retained in three dogs following aggressive medical therapy (two dogs) or 360° conjunctival graft surgery (one dog). Capnocytophaga cynodegmi, Capnocytophaga canimorsus, or unspeciated Capnocytophaga spp. were cultured from corneal samples of all dogs. Long, thin, gram-negative rods were present during cytological evaluation of the cornea in some dogs. Histopathologic evaluation of enucleated globes revealed severe and diffuse neutrophilic and collagenolytic keratitis.

CONCLUSIONS

Capnocytophaga keratitis is a severe, rapidly progressive corneal infection in dogs that is associated with diffuse corneal involvement, extensive keratomalacia, and a relatively poor prognosis. Clinical features of canine Capnocytophaga keratitis are similar to human cases of this infection.

Antibiotic content of selective culture media for isolation of Capnocytophaga species from oral polymicrobial samples

In oral microbiome, because of the abundance of commensal competitive flora, selective media with antibiotics are necessary for the recovery of fastidious Capnocytophaga species. The performances of six culture media (blood agar, chocolate blood agar, VCAT medium, CAPE medium, bacitracin chocolate blood agar and VK medium) were compared with literature data concerning five other media (FAA, LB, TSBV, CapR and TBBP media). To understand variable growth on selective media, the MICs of each antimicrobial agent contained in this different media (colistin, kanamycin, trimethoprim, trimethoprim-sulfamethoxazole, vancomycin, aztreonam and bacitracin) were determined for all Capnocytophaga species. Overall, VCAT medium (Columbia, 10% cooked horse blood, polyvitaminic supplement, 3·75 mg l(-1) of colistin, 1·5 mg l(-1) of trimethoprim, 1 mg l(-1) of vancomycin and 0·5 mg l(-1) of amphotericin B, Oxoid, France) was the more efficient selective medium, with regard to the detection of Capnocytophaga species from oral samples (P < 0·001) and the elimination of commensal clinical species (P < 0·001). The demonstrated superiority of VCAT medium, related to its antibiotic content, made its use indispensable for the optimal isolation of Capnocytophaga species from polymicrobial samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

Isolation of Capnocytophaga species is important for the proper diagnosis and treatment of the systemic infections they cause and for epidemiological studies of periodontal flora. We showed that in pure culture, a simple blood agar allowed the growth of all Capnocytophaga species. Nonetheless, in oral samples, because of the abundance of commensal competitive flora, selective media with antibiotics are necessary for the recovery of Capnocytophaga species. The demonstrated superiority of VCAT medium made its use essential for the optimal detection of this bacterial genus. This work showed that extreme caution should be exercised when reporting the isolation of Capnocytophaga species from oral polymicrobial samples, because the culture medium is a determining factor.

Capnocytophaga spp. involvement in bone infections: a review

Capnocytophaga are commensal gliding bacteria that are isolated from human and animal oral flora and are responsible for infections both in immunocompromised and immunocompetent hosts. Accumulation of microbial plaque, loss of collagen attachment, and alveolar bone resorption around the tooth can lead to local Capnocytophaga spp. bone infections. These capnophilic bacteria, from oral sources or following domestic animal bites, are also causative agents of bacteraemia and systemic infections as well as osteomyelitis, septic arthritis, and infections on implants and devices. The present literature review describes the main aetiologies of bone infections due to Capnocytophaga spp., the cellular mechanisms involved, methods used for diagnosis, antimicrobial susceptibility, and effective treatments.

Three cases of Capnocytophaga canimorsus meningitis seen at a regional hospital in one year

Three cases of meningitis caused by the fastidious Gram-negative rod Capnocytophaga canimorsus have been observed at a regional hospital in 1 y. The difficulties connected with the correct diagnosis by classical culturing methods in contrast to molecular methods, as well as possible reasons for the accumulation of cases, are discussed.

Antimicrobial treatment of Capnocytophaga infections

Capnocytophaga spp. are normal inhabitants of the oropharyngeal flora. They are also involved in periodontal diseases or animal bites, complicated by septicaemia with dissemination to a great variety of sites, both in immunocompetent and immunocompromised hosts. This review will focus on their pathogenesis, spectrum of clinical infections and susceptibility to disinfectants and antibiotics. The spread of beta-lactamase-producing strains limits the use of beta-lactams as first-line treatments, underlying the necessity to test the in vitro susceptibility of clinical strains. Many antimicrobial treatments have been used, despite an absence of randomised studies and guidelines regarding the duration of treatment according to infected sites. Imipenem/cilastatin, clindamycin or beta-lactamase inhibitor combinations are always effective and their use can be recommended in all infections.

First documented Capnocytophaga canimorsus infection in a species other than humans

Capnocytophaga canimorsus was cultured from an infected, dog-inflicted bite wound in a pet rabbit. The wound was treated successfully and the rabbit recovered. To our knowledge, this is the first report of a C. canimorsus infection in a species other than humans.

Capnocytophaga in the dental plaque of immunocompromised children with cancer

OBJECTIVES

(i) To compare the prevalence and levels of Capnocytophaga, a known systemic pathogen in immunocompromised patients, in the dental plaque of healthy children and children with cancer, and (ii) to determine the susceptibility of strains isolated from cancer patients to a range of antibiotics.

PATIENTS AND METHODS

Thirty-one children with cancer undergoing a first course of immunosuppressive chemotherapy and 30 healthy control children were included in the study. Samples were collected on days 0, 7, 14, and 21 of the cure (and equivalent dates in controls). Susceptibility to antibiotics was tested using an agar dilution method and galleries with predefined concentrations of selected antibiotics.

RESULTS

There was a significant drop in the total anaerobic cultivable flora on day 14 and in the prevalence of Capnocytophaga on days 14 and 21 in the children with cancer. The proportion of Capnocytophaga in the anaerobic flora, however, was high in certain cancer patients. Beta-lactam/beta-lactamase inhibitor combinations, imipenem, clindamycin, and tetracycline were the most effective against Capnocytophaga.

CONCLUSION

This study showed that Capnocytophaga decreased in prevalence and proportion in the dental plaque of cancer patients during chemotherapy but became predominant in some cases. It is recommended that imipenem or beta-lactam/beta-lactamase inhibitor combinations be used to treat Capnocytophaga bacteraemia.

Molecular identification of Capnocytophaga spp. via 16S rRNA PCR-restriction fragment length polymorphism analysis

Capnocytophaga spp. have been implicated as putative periodontal pathogens associated with various periodontal diseases. Although the genus is known to contain five human oral isolates, accurate identification to species level of these organisms recovered from subgingival plaque has been hampered by the lack of a reliable method. Hence, most studies to date have reported these isolates as Capnocytophaga spp. Previous attempts at identification were based on biochemical tests; however, the results were inconclusive. Considering the differing virulence features of the respective isolates, it is crucial to identify these isolates to species level. The universal and conservative nature of the 16S rRNA gene has provided an accurate method for bacterial identification. The aim of this study was to identify Capnocytophaga spp. via restriction enzyme analysis of this gene (16S rRNA PCR-restriction fragment length polymorphism). The results (backed up by 16S rRNA gene sequencing) showed that this method reliably identifies all named Capnocytophaga spp. to species level.

Prevalence of oropharyngeal beta-lactamase-producing Capnocytophaga spp. in pediatric oncology patients over a ten-year period

Background

The aim of this study was to evaluate the prevalence of beta-lactamase-producing Capnocytophaga isolates in young children hospitalized in the Pediatric Oncology Department of Hôpital Sud (Rennes, France) over a ten-year period (1993–2002).

Methods

In neutropenic children, a periodic survey of the oral cavity allows a predictive evaluation of the risk of systemic infections by Capnocytophaga spp. In 449 children with cancer, 3,053 samples were collected by oral swabbing and plated on TBBP agar. The susceptibility of Capnocytophaga isolates to five beta-lactams was determined.

Results

A total of 440 strains of Capnocytophaga spp. were isolated, 309 (70%) of which were beta-lactamase producers. The beta-lactamase-producing strains were all resistant to cefazolin, 86% to amoxicillin, and 63% to ceftazidime. The proportion of strains resistant to third-generation cephalosporins remained high throughout the ten-year study, while susceptibility to imipenem and amoxicillin combined with clavulanic acid was always conserved.

Conclusion

These results highlight the risk of antibiotic failure in Capnocytophaga infections and the importance of monitoring immunosuppressed patients and testing for antibiotic susceptibility and beta-lactamase production.

Genetic analysis of an ambler class A extended-spectrum beta-lactamase from Capnocytophaga ochracea

A beta-lactamase gene (cfxA3, 966 bp) was isolated from a beta-lactam-resistant Capnocytophaga ochracea clinical isolate and amplified using primers from the cfxA gene of Bacteroides vulgatus. The MICs of third-generation cephalosporins were much higher than those of the transconjugant Escherichia coli strain. The deduced protein sequence, by comparison with CfxA2 of Prevotella intermedia, had a Y239D substitution and possessed the characteristics of a class A, group 2e beta-lactamase.

Capnocytophaga canimorsus endophthalmitis following cataract surgery

An elderly man developed endophthalmitis 1 week after cataract extraction and lens implantation. Intraocular samples were collected and the patient received intravitreal vanco-mycin and ceftazidime, and topical tobramycin. A Gram stain of vitreous humour revealed spindle-shaped Gram-negative bacilli. He was then given systemic clindamycin and topical ofloxacin. Capnocytophaga canimorsus, a member of the oral flora of dogs and cats, was cultured after 3 days. The infection resolved leaving the patient with a visual acuity of 6/60. An attempt was made to culture the organism from the mouth of the patient's pet dog. This was unsuccessful and the source of the infection remains unknown.

Pneumonia and sepsis due to fluoroquinolone-resistant Capnocytophaga gingivalis after autologous stem cell transplantation

Human oral Capnocytophaga species have been only rarely described as a cause of sepsis in patients following stem cell or marrow transplantation, and pneumonia has not been reported in this setting. In addition, fluoroquinolone resistance is rarely seen in these species, and has never been reported in C. gingivalis. We report a case of pneumonia (confirmed by culture of bronchoalveolar lavage fluid) and sepsis due to fluoroquinolone- resistant Capnocytophaga gingivalis in a patient following autologous stem cell transplantation, who responded to treatment with linezolid and metronidazole. Capnocytophaga infections should be considered in patients with fever following stem cell or marrow transplantation, especially those with neutropenia and mucositis. Susceptibility testing is needed given the existence of multidrug-resistant isolates.

Bacteremia caused by Capnocytophaga species in patients with neutropenia and cancer: results of a multicenter study

We investigated 28 cases of bacteremia caused by Capnocytophaga species that occurred during an 8-year period, most of which were in patients with hematologic malignancy and neutropenia. Infections were uncomplicated, without serious organ involvement and without any apparent source except ulcerations of the oropharyngeal mucosa, and only 1 isolate showed resistance to beta-lactam antibiotics; 9 of 16 isolates were resistant to ciprofloxacin.

In vitro susceptibilities of Capnocytophaga isolates to beta-lactam antibiotics and beta-lactamase inhibitors

The susceptibilities of 43 pharyngeal isolates of Capnocytophaga to beta-lactam antibiotics, alone or in combination with beta-lactamase inhibitors, were tested by an agar dilution method. The 34 beta-lactamase-positive strains were highly resistant to beta-lactams, but the intrinsic activities of clavulanate, tazobactam, and sulbactam against Capnocytophaga, even beta-lactamase producers, indicates that these beta-lactamase inhibitors could be used for empirical treatment of neutropenic patients with oral sources of infection.

Capnocytophaga ochracea: characterization of a plasmid-encoded extended-spectrum TEM-17 beta-lactamase in the phylum Flavobacter-bacteroides

A plasmid-encoded extended-spectrum TEM beta-lactamase with a pI of 5.5 was detected in a Capnocytophaga ochracea clinical isolate. The bla gene was associated with a strong TEM-2 promoter and was derived from bla(TEM-1a) with a single-amino-acid substitution: Glu(104)-->Lys, previously assigned to TEM-17, which is thus the first TEM beta-lactamase to be reported in the phylum Flavobacter-Bacteroides.

DNA-probes for the differentiation of Capnocytophaga species

We designed oligonucleotides to differentiate between the seven currently known Capnocytophaga species. The oligonucleotides were labelled non-radioactively at the 3' end with digoxigenin. The specificity could be demonstrated in a dot-blot hybridization assay by using the type strains, reference strains, and 37 clinical Capnocytophaga isolates as well as 11 representative strains of other taxa as a template. The sensitivity of the assay was calculated with 10(3) bacteria per dot.

Bacteriologic and clinical applications of a new extended-spectrum parenteral cephalosporin

Although third-generation cephalosporins have been considered the backbone of antibiotic therapy for the treatment of many kinds of serious infections, including those in hospitalized patients, lack of activity against some important pathogens still exists among currently available drugs. In addition, increasing accounts of antibiotic resistance, particularly in the hospital environment, are of deep concern and have thus led to the need for the development of newer antimicrobial agents. Cefepime is a now parenteral cephalosporin with an extended spectrum of antibacterial activity that includes both aerobic gram-negative and gram-positive bacteria. It is also active against many gram-negative organisms resistant to ceftriaxone and cefotaxime, as well as many strains of Enterobacter and Citrobacter resistant to ceftazidime. Cefepime appears to be less likely to select out resistant organisms, and it may be less likely to change hospital flora than currently available antimicrobials. Cefepime has been shown to be very well tolerated and effective in the treatment of a variety of infections including moderate-to-severe pneumonia (including cases associated with concurrent bacteremia), complicated and uncomplicated urinary tract infections (also including cases associated with concurrent bacteremia), and skin and skin-structure infections. Clinical response rates are > or = 75% for most infections and have been comparable to ceftazidime in comparative trials. In addition, pretreatment susceptibility testing indicates that >94% of organisms isolated in patients enrolled in clinical trials were susceptible to cefepime.

Susceptibility of Capnocytophaga to antimicrobial agents

A total of 22 clinically isolated Capnocytophaga strains were tested for their susceptibility to antimicrobial agents frequently used in dental practice. All strains were susceptible to penicillin, ampicillin, cefaclor, cefuroxime, erythromycin, clindamycin and tetracycline. Metronidazole had poor activity against most strains.

Bacteremia by multidrug-resistant Capnocytophaga sputigena

A case of bacteremia caused by a multiresistant strain of Capnocytophaga sputigena in a patient with hematological malignancy is described. The strain presented with a pattern of marked resistance to beta-lactams, with MICs of > 256 mg/liter for ampicillin, ticarcillin, piperacillin, cefazolin, and cefuroxime, 64 mg/liter for cefotaxime, and 32 mg/liter for ceftazidime. In addition, the MIC of ciprofloxacin was 16 mg/liter. Both of these groups of antimicrobial agents are frequently used in the empiric treatment of infections in immunocompromised patients. The appearance of resistant strains suggests the need for antimicrobial susceptibility studies in all patients with severe infections caused by Capnocytophaga spp. or other capnophilic organisms present in the oral microflora of these patients.

Antimicrobial susceptibilities and beta-lactamase characterization of Capnocytophaga species

Capnocytophaga species have been associated with a wide variety of infections in both immunocompetent and immunocompromised patients. On the basis of data from antimicrobial susceptibility studies, beta-lactam antibiotics have been considered efficacious therapy. Six of 19 isolates from primarily clinical sources across Canada demonstrated beta-lactamase production, and agar dilution susceptibility testing showed broad resistance to beta-lactam antibiotics. For the beta-lactamase producing isolates, clavulanate reduced the MIC of amoxicillin for 90% of the strains tested by 64-fold. Isolates were highly susceptible to clindamycin, imipenem, and ciprofloxacin. Characterization of the beta-lactamases produced by two of these isolates (Van1 and Van2) was performed. Isoelectric focusing revealed an identical isoelectric point of 5.6 for both enzymes, but they had markedly different relative hydrolysis efficiencies, and different conditions were required to extract the enzymes. This study demonstrates the production of different types of beta-lactamases by Capnocytophaga spp. and suggests the need to screen all clinical isolates of Capnocytophaga spp. for the presence of beta-lactamases.

Characterization of a beta-lactamase found in Eikenella corrodens

Eleven strains of Eikenella corrodens with beta-lactamase activity were isolated from a patient with refractory periodontitis who had previously been treated with penicillin antibiotics. These strains were relatively resistant to benzylpenicillin, amoxicillin, and ampicillin (MICs, greater than or equal to 64 micrograms/ml); susceptible to amoxicillin-clavulanate (2:1) (MICs, less than or equal to 4 micrograms/ml); and moderately susceptible to cephalothin and cephaloridine (MICs, 0.12 to 16 micrograms/ml). The addition of 1 microgram of potassium clavulanate, a beta-lactamase inhibitor, per ml resulted in a significant increase in the susceptibilities of these strains to penicillins but not to cephalosporins. Potassium clavulanate had no effect on non-beta-lactamase-producing strains. Enzyme production was constitutive since activity was not increased when cells were cultivated in the presence of benzylpenicillin. Enzyme activity was strongly inhibited by potassium clavulanate, sulbactam, and iodine; weakly inhibited by cloxacillin, imipenem, and moxalactam; but not inhibited by aztreonam, EDTA, or p-chloromercuribenzoate. By gel infiltration, the enzyme had an estimated molecular mass of 29 kDa. Isoelectric focusing of the partially purified enzyme gave a major beta-lactamase band at pH 5.50 and a minor band at pH 5.60. Plasmids were not detected in any of the 11 beta-lactamase-positive strains. This enzyme is considered to belong to class 2a of the Bush classification scheme.

Novel beta-lactamase from Capnocytophaga sp

A novel beta-lactamase activity which confers resistance to expanded-spectrum cephalosporins and penicillins has been found in strain IC 5/21 of Capnocytophaga spp. Enzyme activity migrated at a molecular size of 38,000 daltons and at an isoelectric point of 3.6, with a minor band at 4.1. Kinetic studies suggested that it belonged to Richmond and Sykes beta-lactamase class 1c. Isoelectric focusing could be achieved only if a nonionic detergent was added to the gel, suggesting the presence of a hydrophobic enzyme akin to a membrane-bound beta-lactamase of gram-positive bacteria. The location of the gene coding for this beta-lactamase is not yet known.

Fluoroquinolone antimicrobial agents

The fluoroquinolones, a new class of potent orally absorbed antimicrobial agents, are reviewed, considering structure, mechanisms of action and resistance, spectrum, variables affecting activity in vitro, pharmacokinetic properties, clinical efficacy, emergence of resistance, and tolerability. The primary bacterial target is the enzyme deoxyribonucleic acid gyrase. Bacterial resistance occurs by chromosomal mutations altering deoxyribonucleic acid gyrase and decreasing drug permeation. The drugs are bactericidal and potent in vitro against members of the family Enterobacteriaceae, Haemophilus spp., and Neisseria spp., have good activity against Pseudomonas aeruginosa and staphylococci, and (with several exceptions) are less potent against streptococci and have fair to poor activity against anaerobic species. Potency in vitro decreases in the presence of low pH, magnesium ions, or urine but is little affected by different media, increased inoculum, or serum. The effects of the drugs in combination with a beta-lactam or aminoglycoside are often additive, occasionally synergistic, and rarely antagonistic. The agents are orally absorbed, require at most twice-daily dosing, and achieve high concentrations in urine, feces, and kidney and good concentrations in lung, bone, prostate, and other tissues. The drugs are efficacious in treatment of a variety of bacterial infections, including uncomplicated and complicated urinary tract infections, bacterial gastroenteritis, and gonorrhea, and show promise for therapy of prostatitis, respiratory tract infections, osteomyelitis, and cutaneous infections, particularly when caused by aerobic gram-negative bacilli. Fluoroquinolones have also proved to be efficacious for prophylaxis against travelers' diarrhea and infection with gram-negative bacilli in neutropenic patients. The drugs are effective in eliminating carriage of Neisseria meningitidis. Patient tolerability appears acceptable, with gastrointestinal or central nervous system toxicities occurring most commonly, but only rarely necessitating discontinuance of therapy. In 17 of 18 prospective, randomized, double-blind comparisons with another agent or placebo, fluoroquinolones were tolerated as well as or better than the comparison regimen. Bacterial resistance has been uncommonly documented but occurs, most notably with P. aeruginosa and Staphylococcus aureus and occasionally other species for which the therapeutic ratio is less favorable. Fluoroquinolones offer an efficacious, well-tolerated, and cost-effective alternative to parenteral therapies of selected infections.

The effect of subminimal inhibitory concentrations of antimicrobial agents on three bacterial mixtures

A test tube technique was developed to screen bacterial mixtures to detect interbacterial interactions that play a role in determining sensitivity to antimicrobial agents. We found 3 mixtures where these bacterial interactions change the sensitivity to antimicrobials or change the proportions of each bacterial species in the mixture. The mixtures were: Fusobacterium nucleatum 102.3 and Bacteroides endodontalis ATCC 35406; F. nucleatum 102.3 and B. endodontalis BN11 a-f; and Capnocytophaga ochracea 1956c and Eubacterium saburreum 162.4. The antimicrobials used were metronidazole for the first 2 mixtures and tetracycline for the last. F. nucleatum seems to protect B. endodontalis from the action of metronidazole. Conversely, the growth inhibition of C. ochracea by E. saburreum was lifted when tetracycline was present. We also found that the growth of C. ochracea can then permit the subsequent growth of E. saburreum. The test tube method permits the evaluation both of interbacterial interactions and the detection of any protective mechanism against antimicrobial agents in a bacterial mixture. We found that F. nucleatum 102.3 can decrease the metronidazole level in the culture medium, and by the use of 14C-metronidazole we demonstrated that acetamide is produced from metronidazole.

Susceptibility testing of Danish isolates of Capnocytophaga and CDC group DF-2 bacteria

Twelve Capnocytophaga and seven DF-2 strains were tested for their susceptibility to 14 antimicrobial agents using an agar dilution and an agar diffusion method. Twenty-three other antibiotics were evaluated using the diffusion test only. All strains were fully susceptible to penicillin, ampicillin, cefuroxime, cefotaxime, erythromycin, clindamycin, chloramphenicol, doxycycline, rifamycin and ofloxacin using both methods. Clindamycin, rifamycin and cefotaxime were most active. Using agar dilution some strains were susceptible to gentamicin, but agar diffusion showed total resistance. One Capnocytophaga strain was susceptible and another moderately susceptible to metronidazole, other strains were resistant. The agar diffusion test showed that both Capnocytophaga and DF-2 were resistant to most other aminoglycosides, to fosfomycin, polymyxin and trimethoprim. All strains of both taxa were fully susceptible to piperacillin, cefoxitin, imipenem and fusidic acid and showed different susceptibilities to the other agents. Susceptibility testing by means of agar diffusion using an enriched chocolate agar and 5% CO2 atmosphere could be used to test Capnocytophaga and DF-2 strains and gives sufficient accuracy for routine use, when revised inhibition zone breakpoints are employed.

In vitro susceptibility of 96 Capnocytophaga strains, including a beta-lactamase producer, to new beta-lactam antibiotics and six quinolones

The in vitro activities of new beta-lactam antibiotics and new quinolones were studied against 96 Capnocytophaga strains, including a beta-lactamase-producing strain which was resistant to ampicillin, amoxicillin, carbenicillin, cephalothin, and cefamandole. All strains were susceptible to the combination of amoxicillin and clavulanic acid, ureidopenicillins, cefoxitin, broad-spectrum cephalosporins, and imipenem. Cephalothin and cefamandole did not show good activity against most strains. All Capnocytophaga spp. were uniformly susceptible to the five new quinolones tested.